1. Field of the Invention
This invention relates to a zoom lens system, and more particularly to an improved zoom lens system wherein the focal length thereof is varied while maintaining the resultant image position always in the stationary image plane throughout the range.
2. Description of the Prior Art
There are known two types of zoom lens system. The zoom lens system is comprised of, for instance, as shown in FIG. 1, a front fixed lens component I, a zooming movable lens component II, a compensating movable lens component III, and relay fixed lens components IV and V. In one type of the zoom lens system, the front fixed lens component I is moved axially when taking a close-up photograph. In the other type, all the other four components or some of the other four components are axially moved when taking a close-up photograph. In the former type of the zoom lens system, the focus is maintained at a constant position. However, when taking a photograph of an object extremely close to the lens system, the front fixed lens component should be moved by an extraordinarily long distance and consequently light passing through the lens system does not reach the marginal portion of the film on the image plane in the camera. On the other hand, in the latter type of the zoom lens system which is called "macro-focus type zoom lens", it is easy to take a photograph of an object located extremely close to the lens system. However, the resultant image position is changed as the focal length thereof is changed in this type.